1. Field of the Invention
This invention relates to a process for drying fruit and/or preserving dried or other fruits that are rich in sugar, such as the d'Agen prune.
The purpose of this invention is to provide a process that avoids the phenomenon known as "efflorescence of prunes" or sugaring.
2. Description of the Prior Art
This phenomenon, which can be observed as an irregular and superficial powdering, especially during storage and preservation of prunes after the drying process, seems to result from a change in the metabolism of the sugars present in the fruit, mainfesting itself in the following sequence linked to the enzymatic action:
1. superficial crystallization,
2. a change in the color of the sugars crystallized on the surface,
3. finally, alcoholic fermentation.
Since this invention is particularly, though not exclusively, aimed at the processing of prunes, a brief review of the conventional procedure for drying and storing prunes is first presented.
The dessication of prunes takes place in continuous-drying tunnels under controlled temperature, atmospheric humidity, and ventilation.
After this process, which is performed at a temperature in the range of 55.degree. to 80.degree. C., depending on the type of tunnel used and the "cooking" stage of the fruit, and lasts an average of 24 hours, the prunes are sized and stored for fairly long periods before conditioning.
The prune being very hygroscopic, the level of humidity is most important; so too, is storage in an environment that is as isothermal as possible and protected from light.
Moreover, to assure good preservation, it is important that the water content of the prune does not exceed 23 percent.
The conditioning, consists of giving a gloss and tenderness to the prunes while assuring that they are perfectly preserved. To achieve this, rapid and direct rehydration is performed, either by steam or by soaking in water at 75.degree. to 80.degree. C. for a time varying from 5 to 20 minutes. Thus, prunes are obtained that are ready to eat as such or to be cooked, having a water content between 29 and at most 35%, in accordance with prevailing law.
Preservation is assured either by sterilization, after packaging, or by adding a very small quantity of sorbic acid in the rehydration bath, before packaging. The packaging can take many forms, such as cardboard boxes, plastic bags, wooden crates, metal boxes, glass jars, etc.